With the continuous increase in switching frequency of the switching power of the pulse width modulation (PWM) technology, it causes a generation of an electromagnetic interference. The electromagnetic interference peak values of the switching transformer concentrate on frequency-multiplication points of the switching frequency. Since it is a discrete spectrum which uses the switching frequency as a basis frequency, those harmonic components are transmitted outwardly by transmitting lines and a space electromagnetic field and transmission and radiation interference issues are generated accordingly. It not only seriously pollutes the surrounding electromagnetic environment, but also causes the electromagnetic interference to nearby electrical equipment. In a conventional technology solution, in order to decrease the electromagnetic interference of the switching transformer, it usually employs a small amount of resistors, capacitors and some integrated operational amplifying elements to implement. Furthermore, PWM integrated circuit employs fixed modes, which are not able to be adjusted according to the variations of heavy and light loadings. Under a heavy loading condition, a serious electromagnetic interference is generated since a larger current change and a larger change of a voltage ripple.